thermodynamics, the word exothermic "outside heating" describes a process or reaction that releases energyusually in the form of heat, but it can also release energy in form of light (e.g. explosions), sound, or electricity (e.g. a battery). Its etymology stems from the Greek prefix "exo-," meaning “outside” and the Greek word "thermein", meaning “to heat”. The term “exothermic” was first coined by Marcellin Berthelot. The opposite of an exothermic process is an endothermicprocess, one that absorbs energy in the form of heat.
The concept is frequently applied in
physical sciencesto chemical reactions, where chemical bond energyis converted to thermal energy(heat).
Exothermic refers to a transformation in which a system releases energy (heat) to the surroundings:
:Q < 0
When the transformation occurs at constant pressure:
:"∆H < 0"
and constant volume:
:"∆U < 0"
adiabaticsystem (e.g. a system that does not give off heat to the surroundings), an exothermic process results in an increase in temperature. [cite book | last = Perrot | first = Pierre | title = A to Z of Thermodynamics | publisher = Oxford University Press | year = 1998 | id = ISBN 0-19-856552-6 ]
In chemical reactions, the heat that is released is in the form of electromagnetic energy. The loss of kinetic energy via reacting electrons causes light to be released. This light is equivalent in energy to the stabilization energy of the energy for the chemical reaction, i.e. the bond energy. This light that is released can be absorbed by other molecules in solution to give rise to molecular vibrations or rotations, which gives rise to the classical understanding of heat. In contrast, when endothermic reactions occur, energy is absorbed to place an electron in a higher energy state, such that the electron can associate with another atom to form another chemical complex. The loss of energy within solution is absorbed by the endothermic reaction and therefore is a loss of heat. This is the physical understanding of exothermic and endothermic reactions within solution.
Some examples of exothermic processes are: [ [http://antoine.frostburg.edu/chem/senese/101/thermo/faq/exothermic-endothermic-examples.shtml Exothermic - Endothermic examples] ]
* Condensation of rain from water vapour
* Combustion of
fuels such as wood, coaland oil
* Mixing water and
* The setting of
polymerisationreactions such as the setting of epoxy resin
Implications for chemical reactions
Chemical exothermic reactions are generally more spontaneous than their counterparts,
endothermic reactions. In a thermochemical reaction that is exothermic, the heat may be listed among the products of the reaction.
Differential scanning calorimetry
* http://chemistry.about.com/b/a/184556.htm Observe exothermic reactions in a simple experiment
Wikimedia Foundation. 2010.